Recently, wireless technologies have exploded into the marketplace with uses ranging from globe spanning satellite systems to local area networks. Many of these wireless systems use frequency division multiple access (FDMA), time division multiple access (TDMA) or code division multiple access (CDMA) multiplexing schemes for maximizing the capacity of from a given communication spectrum bandwidth.
CDMA systems do not separate signals according to frequency or time slots, but instead allow the signals to occupy the same bandwidth at the same time. Before the digital CDMA signals are commingled at the transmitter, each is processed by being exclusive-ORed (added modulo 2) to a different pseudorandom noise sequence. At the receiver for each channel, the signals are recovered by again exclusive-ORing the demodulated signal with the same pseudorandom noise sequence used during the encoding process. The pseudorandom noise sequences are all mutually orthogonal so that after receiving the encoded signal, the shared traffic in the channel sounds like random noise. As the channel usage increases, the signal-to-noise ratio degrades.
The specification for CDMA systems, Interim Standard No. 95 (IS-95) of the Telecommunications Industry Association (TIA), Arlington, Va. provides for two compression ratios for digitalized speech. One has a peak data rate of 8 kbps, the other 13 kbps. The former yields higher capacity, while the later produces higher voice quality. The CDMA systems regulate system power very precisely so that signals transmitted from mobile stations located near the base station do not overwhelm those signals transmitted from mobile stations at greater distances from the base station. The objective is to have all the signals arrive at the base station at approximately the same power level. Thus, services offered by a wireless environment should be transparent to those offered by a POTS environment.
As usage of wireless technology increases at a geometric rate, less technically sophisticated users become a larger percentage of the customer subscriber base. There exists a need for wireless technologies to emulate the features that are commonly found in the wireline environment (plain old telephone service (POTS) with enhanced services). Implementation of the wireless features by the customer subscriber is desired to have an interface that closely resembles the operation of the feature in a POTS environment.
The implementation of a dial tone for use with certain features such as call forwarding provides a transparent interface between plain old telephone service (POTS) and wireless environments. Eventually, new technologies will allow a wireless telephone to convert to a cordless telephone linked to an in home base station, provided the user is within a particular range of the base station. The implementation of this technology is often referred to as wireline, wireless wireline, wireline replacement, wireless local loop, and wireless local access service. Upon transfer from a cellular environment to a cordless environment, a transfer occurs switching the call from a mobile switching system to the public switched network. When this occurs, users will probably be charged a substantially lower per minute usage rate costs when using the public switched telephone network than when operating in the wireless environment. In addition, wireline service will provide increased user flexibility. However, the transition between the wired environment and the wireless environment requires a seamless, transparent interface. Invoking of calling features such as call forwarding and three way calling will need to be initiated in the same manner regardless of whether the call is made using the public switched telephone network or a wireless network.